Biodiesel is becoming an increasingly important alternative to petroleum based fuels. Biodiesel includes a fatty acid methyl or (ethel) esters (hereinafter referred to as FAME) produced from trigylcerides as the product of vegetable, lipid, animal, trapped grease, or recycled cooking oil (collectively referred to herein as WCO). Biodiesel is becoming an important alternative fuel for a variety of reasons. For example, biodiesel may be compatible with traditional petroleum-based diesel internal combustion engines with little to no modifications being necessary. Additionally, combustion of biodiesel in internal combustion engines is generally cleaner burning than petroleum based diesel and produces less emission of particulate matter, carbon dioxide, sulfur dioxide, and organics compared to petroleum based diesel. Moreover, because biodiesel can be produced using waste materials, it is environmentally friendly.
One of the limitations associated with biodiesel is related to the manufacture of biodiesel. Biodiesel is essentially produced in batch or continuous reactors through a transesterification (or two-step esterification-transesterification) reaction under homogenous, heterogeneous or enzymatic catalyst. It can also be produced at supercritical conditions without catalyst due to the enhanced solubility of the mixture; however, these conditions are least favorable due to a high energy penalty necessary to maintain the supercritical conditions.
In a batch process, the WCO and methanol are brought together in a batch reactor while subjected to a continuous impeller mixing. As the reaction proceeds toward completion, the product is drained to a separation reservoir forming two distinct layers of products (FAME and glycerol) that can be easily separated. Unfortunately, the batch process suffers from high operating costs, reduced throughput, and increased product quality variation.
In known continuous processes, a tubular configuration is used where the reactant is continuously pumped into the reactor. To enhance the reaction, the configuration must allow an increase in surface area per unit volume, efficient entrainments and mixing to enhance mass transfer, and component solubility at low pumping power. Small flow rates can lead to stratified or laminar, two phase flow resulting in mass transfer limitations. High flow rates result in shorter residence time and high head loss. As a result, there is a need for a reactor design which is not mass transfer limited and which minimizes pumping loss, while increasing throughput and yield.